How does send and return really work?

Manfred-Klose · 2008-08-28T22:14:46+00:00

How does send and return work on a full valve amplifier? No one gave ever gave me a straight answer, i'll guitarforum a try. All i want to know is when the...

How does send and return really work?

Manfred-Klose

SAy i am going to boss route(CH-1,DD-6,OC-3) would that match the level coming out of the send loop?

(+4db)???

I like your diagram, very handy.

teleplayer

I know my amp (Vox ac30) has a level switch for the fx loop, so i can lower it down to -10bB (could be -20dB don't have my amp nxt to me, i'm at work) or have it at +4dB... See if u have that, rack stuff should handle +4 perfectly (depending on what stuff u have of course) but i wouldn't bang that through my pedals

AlanRatcliffe

SAy i am going to boss route(CH-1,DD-6,OC-3) would that match the level coming out of the send loop?

No! I know for a fact that Bothner's workshop sees a lot of Boss pedals (particularly the DDs and the RVs) with fried input circuitry because guys have tried using them in loops on amps and mixers.

I can't remember the exact figures (I've always had problems remembering all the ins and outs of decibels), but the difference between -20dB and +4dB is huge - remember, every 3dB is double the power.

I know my amp (Vox ac30) has a level switch for the fx loop, so i can lower it down to -10bB (could be -20dB don't have my amp nxt to me, i'm at work) or have it at +4dB...

Yeah, which is a nice feature. It might be -10dB (which is the hi-fi reference level), most pedals have the headroom to handle that.

Manfred-Klose

So if i dont have rackmount units, i dont even have to bother putting pedals in the signal chain, I dont want to fry my pedals!!!!

Scary, i'll go look in the catoloque of my amp, and check out the specs of the send/return loop.

Manfred-Klose

I just checked out the specs.

From the send its -6dbV at 0.5 volt RMS, and the same for return.

AlanRatcliffe

Odd figure! You'd have to check the pedals specs or contact the manufacturer to find out if it can handle those levels.

Manfred-Klose

Will do so.

The reason why the amp is odd, is because it is made in mississippi(the home of the blues), where they probably never bothered use the send and return anyway, they just played the blues all day long.........

Manfred-Klose

just joking, but it wouldbe a cool storie to tell.

FenderBender

You forgot to mention the Jack Daniels' part in all this!
You're welcome to send a link for, or scan and send me the spec section of each pedal's manual and I'll take a look so long.

Manfred-Klose

I going to do some reasearch on this subject.

The pedals i am planning to put in the FX loop is Boss CH-1, Boss DD-6.

FenderBender

Great, give me a while to settle the family and other delinquent acquaintances and I'll do some checking up.

Renesongs

You forgot to mention the Jack Daniels' part in all this!

Doesn't Jack come Kentucky - they got their own blues their - call it Blue-Grass - I reckon the specs on you amp being strange has less to do with the blues and more to do with grass.

Manfred-Klose

right on rene!!

FenderBender

Hi Manfred,

My apologies for taking so long to get back to you. I had a long look at the specs of the pedals and the diagram of your amp.

The levels we have to consider in your setup are:

-6dBV (amp effects loop) = 0.501Vrms = 0.706Vpeak
-20dBu (DD-6 pedal cct) = 0.077Vrms or 0.108Vpeak

We can more or less calculate the peak instantaneous power dissipated by the input stage of the pedals when fed by the amp using Ohm's law:

P=V2/R = (0.7062)/1000000 = 5*10-7W or 0.5 microwatts, of little threat to your pedals input stage.

The impedance of the amp's "effects return" input stage is (you guessed it!) 1Mohm. Although the signal level sent from the pedals is a lot less than specified in your manual, the amp is equipped with feedback from the output transformer's secondary winding that is used to regulate the bias on the cathode of the first valve in the main amp circuit. This should take care of varying signal levels.

IMO you are ok electrically, but you will have to listen to it and decide if works for you or not.

FenderBender

Take a look at http://www.sengpielaudio.com/calculator-db-volt.htm for a signal conversion calculator and tips.

Manfred-Klose

Hey graeme its not the end of the world, seems we are the only ones scrolling the internet at 2 in the morning.

lucky me i studied Electrical engineering at shcool, so know know a little bit about these things.
How did you get all your knowledge about electrical circuits? library,internet,college......

Thanks for the time you took.

How would the send and return differ for say a marshall jcm900?
I just went and looked at the circuit, and the send and return configuartion seems similar.

GO check out some of these sites for Schematics on almost everything:
http://www.schematicheaven.com/index_HTML.htm
http://www.freeinfosociety.com/electronics/schempage.php?cat=1

I gave the shcematics of the jcm800 to one of my buddies, and he is building his own marshall, thats intense.

AlanRatcliffe

Good links guys, I'm bookmarking frantically here!

Manfred-Klose

One day when i have the knowledge, i'd rather build my own amp,than to pay R20 000+ for a boutique amp.

Anyone with me on that on?

MiKeZilLA

One day when i have the knowledge, i'd rather build my own amp,than to pay R20 000+ for a boutique amp.

Anyone with me on that on?

Yep i'd much rather have you build me one too... ?

FenderBender

Hey graeme its not the end of the world, seems we are the only ones scrolling the internet at 2 in the morning.

Yeah I'm really addicted! I only ever put my time into things I really enjoy....most of my time that is ?

How did you get all your knowledge about electrical circuits?

I started pottering around with electronics in 1983 and then studied EELC at CPUT in the late 80s. After that I worked in the consumer electronics sector repairing video cameras and then moved to the industrial sector in 1994. My last position was the electrical manager for a large packaging producer...until being retrenched at the end of July.

Thanks for the time you took.

Well thanks for giving me something to get my teeth into ?

How would the send and return differ for say a marshall jcm900?

I'll take a look and get back to you ?

I gave the schematics of the jcm800 to one of my buddies, and he is building his own marshall, thats intense.

Thats lekker!

One day when i have the knowledge, i'd rather build my own amp,than to pay R20 000+ for a boutique amp.

Anyone with me on that on?

Bring it on! I have plenty time on my hands lately, hence getting into guitar and related equipment. I'd be very game to put together a kickass amp project with any willing parties. I have a good gut feeling that I should be doing exactly what I am doing. It has already been far more rewarding in such a short space of time as opposed to 5 years in a (thankless) production environment ?